Question

The activity of lateral meristems ___________ older roots and stems. a. lengthens b. thickens c. both a and b d. has no effect on

Short answer

Lateral meristems thicken older roots and stems.

Step-by-step solution

Identify Lateral Meristem Function

Lateral meristems are responsible for the secondary growth of plants. They increase the girth or thickness of roots and stems by producing new cells.

Understand Growth in Context

Secondary growth contrasts with primary growth, which results in lengthening of the plant. For older roots and stems, secondary growth predominantly occurs.

Matching Activity with Function

Since lateral meristems are involved in thickening, the correct term to describe their effect on older roots and stems is 'thickens.'

Key concepts

The Role of Secondary Growth

In plants, growth occurs through two main processes: primary and secondary growth. Primary growth refers to the elongation and vertical extension of plants, which is primarily due to the activity of **apical meristems**. These are found at the tips of roots and shoots, where they facilitate the lengthening process.
Secondary growth, on the other hand, occurs as a result of the activity of **lateral meristems**. This growth is crucial as it contributes to the increase in thickness or girth of the plant, particularly in the older sections of roots and stems. Unlike the length-focused primary growth, secondary growth allows the plant to become sturdier, supporting extra weight and generating new tissue required for the plant's stability and nutrient transportation.
Two types of lateral meristems are involved in secondary growth: the **vascular cambium** and the **cork cambium**. The vascular cambium produces new layers of vascular tissue, which includes xylem and phloem, critical to moving water and nutrients throughout the plant. Meanwhile, the cork cambium produces cork cells that contribute to the protective bark of trees. This overarching secondary growth enhances the plant's ability to thrive as it matures.

Understanding Plant Anatomy

Plant anatomy revolves around the intricate structures that make up a plant, focusing on how these structures enable growth and survival. Key components in plant anatomy include:

• **Meristems**: These are regions of undifferentiated cells that are capable of division and growth. They facilitate both primary and secondary growth in plants.
• **Root System**: Comprised of roots that anchor the plant and absorb water and minerals from the soil. In older roots, secondary growth results in an increase in diameter.
• **Shoot System**: Includes stems and leaves. Stems support leaves and flowers, while leaves are the centers for photosynthesis.

The interplay between these parts illustrates how plants maintain their structural integrity. The key to understanding plant anatomy lies in recognizing the functions and interactions of these components. As plants grow, not only do they extend upward and downward through primary growth, but they also expand outward via secondary growth, exemplifying a well-coordinated growing process that ensures both stability and the capacity to survive in varying environments.

Root and Stem Thickening

Root and stem thickening is a critical aspect of plant development, particularly for perennials and other long-lived plants. This thickening is a result of secondary growth facilitated by lateral meristems.
During secondary growth, the vascular cambium generates additional layers of xylem and phloem. This leads to an increased diameter in stems and roots. The xylem, which is produced more profusely compared to phloem, primarily contributes to the plant's increased girth due to its woody nature.
The cork cambium, another lateral meristem, complements this thickening by producing the protective cork layer. This cork is essential as it serves as a barrier against pests and disease, while also preventing water loss.
Thus, the thickening of roots and stems enhances a plant's ability to sustain itself over time, offering protection and a robust framework to support necessary plant functions. It allows trees to grow tall and wide, providing them with the strength to endure environmental pressures.